Rare orchid species in Malaysia: New records, recollections and amended descriptions

Paphiopedilum exul, Calanthe chrysoglossoides, and Luisia brachystachys are reported here as new records for Malaysia, whereas Bryobium cordiferum subsp. borneense, Habenaria rostellifera, and Taeniophyllum rugulosum are three rare orchid species recollected from Sarawak, Perlis, and Perak, respectively. This paper highlights brief descriptions and photographic illustrations of each species for easy identification. Besides, notes on morphological comparisons with the closely related species and artificial taxonomic keys are included as well.


Introduction
Southeast Asia including Peninsular Malaysia and Borneo spans about 3% (4.5 million km 2 ) of earth's total land area that harbours approximately 20-25% of earth's higher plant species [1,2]. Substantial anthropogenic habitat alterations, forest fires, and the overexploitation of wildlife in the said vast region are detrimental to its biodiversity [3]. Malaysian vegetation comprises evergreen, montane, mixed deciduous, heath and alpine, limestone, and ultramafic forests supporting a wealth of plant diversity [4]. Worth mentioning is the northernmost corner of Peninsular Malaysia, including Perlis and Kedah, bordered by Thailand in the north constitutes a significant component of the Thai and Burmese flora [5][6][7]. The forests lie mainly on hilly terrain of limestone, which is part of the Setul and Chuping limestone formation with unique geological formation and high level of flora endemism [8,9]. However, these forests are declining rapidly because of forest clearance for quarries, timber extraction and other forms of agricultural and infrastructure developments [7,[10][11][12]. Thus, uncountable number of the plant species may have gone extinct.
Orchidaceae is the most abundant flowering plant family in Malaysia. Approximately, 978 species recorded in Peninsular Malaysia [13-19] and 3,000 species have been recorded in Sabah and Sarawak [13]. Major collective records of Malaysian orchid species were monographed by many botanists, including R. E. Holttum [20], H. N. Ridley [21], J. J. Smith [22], J. J. Vermeulen [23], I. M. Turner [24], G. Seidenfaden, and J. J. Wood [25]. In the past two decades, several studies on the orchid diversity covering various elevation gradients and vegetation types in Malaysia involved local conservationist. Of these, the most significant studies on Malaysian orchids include [12,14,[26][27][28]-limestone forest; [13]-peat swamp forest; [29,30]-hill forest; [31]-lowland forest; [32][33][34][35][36]-montane forest; [37]-coastal heath forest; [38,39]-logged forest. Judging by these past and recent works on orchid flora in Malaysia, it is apparent that Malaysia possesses one of the world's richest orchid floras in one of the largest remaining areas of tropical rainforest in the Old World. Undoubtedly, there are more species still awaiting discovery in the remaining extensive forests of Peninsular Malaysia and Borneo. We are reporting new orchid species to the flora of Malaysia and recollection of additional two rare species aimed at elucidating the diversity of orchids in Malaysia. The rare taxa were found and identified whilst working on the diversity and conservation of wild orchids in the undisturbed and disturbed forests of Malaysia. This paper provides brief description, taxonomic notes, relevant notes on ecology and distribution, morphological comparisons with the closely related species, artificial taxonomic keys, and photographs to facilitate easy identification of these species in the field. . Living specimens were transplanted into an ex-situ conservatory, and then further nurtured into identifiable samples. The complete specimens were processed using standard herbarium preparation technique of [40]. Our locality data are withheld to protect the populations from illegal collections. Prior to the morphological examination, methylated spirit-preserved and fresh flower specimens were dissected, described and photographed under AM4113ZT Dino-Lite Digital Microscope. Alpha taxonomy with reference to the type specimens, monographs and protologues was employed in the identification process, evaluation of the species' distribution status, and a comparative morphology study with the closely similar species. Digitised images of herbarium collections, botanical drawing and records deposited in National Herbarium of the Netherlands (NHN) accessed through Browse Dutch Natural and petals pubescent with short white and dense indumentum, greenish white in general, sepals suffused green, petals greenish brown with clear dark brown veins arching towards apex, pouch showy and glossy reddish-purple pouch hooded by dorsal sepal. Dorsal sepal 3.4 × 2.7 cm, cucullate, broadly ovate; apex cuspidate, folded, recurved, ca. 5.5 mm long; base rounded; ventral side white suffused yellowish brown, glossy dark brown spots; spots suffused over lower half from basal to the central area, arranged in lines, contrast with the yellow background; dorsal side suffused green, blotched dark brown at base, sparsely hairy; prominent, raised median outer keel covered by dark brown hairs; margin white, entire, covered by dense white indumentum. Synsepalum 3.5 × 2.1 cm, cucullate, ovate, apex obtuse, base cordate, yellowish green, venation green, bordered white, margin covered by dense white indumentum, back side outwardly keeled, suffused green, blotched dark brown at base as in dorsal sepal. Petals 3.4 × 1 cm, more than twice as long as wide, outspread, almost horizontally, oblanceolate, apex obtuse, margins undulate and minutely hairy, proximally black hairs occur on surface at the base, greenish brown at both sides, suffused green towards apex and margins, prominent reddish brown at inner side, minutely spotted at base, recurved forward around the pouch. Pouch or labellum 2.8 × 1.4 cm, slipper-shaped, side lobes rectangular, incurved, glossy, reddish green, pale green at mouth, venation brown, hairy interior at the nectary and dorsal opening. Staminode 8 × 8 mm, obovate, yellowish green, verruculose, hairy, indumentum dark brown, indumentum much longer near the base of the gymnostemium, apex mucronulate, central teeth rounded, base connate to the gymnostemium, anthers and stigma hidden behind staminode, margin slightly recurved; fovea 2 × 0.9 mm, narrowly ovate, yellow, bears a shiny bright yellow knob-like wart at base (umbo); anthers 2, positioned on either one side, 2.5 × 1.4 mm; stigma ca. 4.7 mm, widely ovate. Pollinia 2, 2 × 1.3 mm; gymnostemium ca. 5 mm.

Materials and methods
Distribution. It was an endemic species to limestone cliffs on the east side of the Phuket-Krabi Gulf of Peninsular Thailand [41,42]. In Peninsular Malaysia, the specimen of the first record reported in this paper was collected from Perlis (Fig 2). The exact locality is withheld in this paper to protect the population from illegal collections. P. exul were also reported seen in Kedah, however, we have no authentic specimens to substantiate this claim.
Etymology. In Greek, Paphos means birthplace of the mythological goddess Aphrodite; and pedilon means slipper, referring to the slipper-shaped labellum [43]. The species epithet, exul was derived from an English word 'exile' by Ridley means 'banished one' because of the geographical isolation from the closely allied one, P. insigne (Wall. ex Lindl.) Pfitzer [43]. Hence, the common name, Excluded Paphiopedilum.
Habitat and ecology. It grows on the cliff in a limestone hill forest, dried but shaded (Fig 3).
Taxonomic notes. The newly recorded P. exul belongs to subg. Paphiopedilum sect. Paphiopedilum. Subg. Paphiopedilum sect. Paphiopedilum characterised by having single flowered (or at most 2-flowered), linear or spathulate petals that are more than twice as long as broad, pouch side lobes incurved, and strap-shaped and plain green leaves [44]. Paphiopedilum exul has been described by several authors under different names due to the wide variation in pouch, staminode and dorsal sepal morphologies. This species closely resembles P. insigne, but has smaller flowers and belongs in its alliance [45]. The former species differs by having sepals shorter (3.2-3.8 cm vs 5-6.4 cm) [46], staminode apex apiculate instead of emarginated and roundly bilobed, and anthers hidden behind the staminode [47]. In [47], P. exul differs by having the leaves surface yellowish rather than glaucous as in P. insigne. However, this character is rather unreliable as leaf colouration changes depending on the habitat and ecological conditions. Plants found in Perlis has slight variations in dorsal sepal and petals and staminode morphologies if compared to the one found in Peninsular Thailand (see Table 1). The base connate to the gymnostemium rather than bilobed and free as illustrated in [47], and the sepals are shorter [46]. Also, the peculiarity seen at the flower size (Table 1). Minor variation in staminode shape, flower size, and leaf pattern across localities are common in Paphiopedilum [44,48,49]. Paphioepdilum exul is having no near allies among the Peninsular Malaysian species. It is easily distinguishable if compared to the other single-flowered with long and spotted petals Paphiopedilum, such as P. barbatum (Lindl.) Pfitzer, P. bullenianum (Rchb.f.) Pfitzer, and P. callosum var. sublaeve (Rchb.f.) P.J.Cribb.
Etymology. The genus name, Calanthe is from the Greek kalos, means beautiful, and anthos, means flower, in reference to the showy flowers of the type species, whereas the species epithet chrysoglossoides is derived from Greek chrysous, golden, and glossa, tongue, alluding to the colour of the labellum in the type species [43].
Habitat and ecology. Growing in a shaded lower montane forest at elevation ca. 1,000 m. An undisturbed forest area but connected to a highly developed area for hotel and shopping complexes.
Taxonomic notes. Calanthe chrysoglossoides is similar to C. monophylla Ridl. and C. taenioides J.J. Sm. that occur in montane forests and belongs to sect. Monophylla. The two species were the only representative of the single-leaved Calanthe found in Peninsular Malaysia. In comparison, the species are having a creeping rhizome and only one full-sized leaf to a pseudobulb, except C. chrysoglossoides has larger flowers with broader sepals and petals, and ovate or almost circular labellum midlobe instead of narrow or bilobed at apex. Artificial key to Calanthe sect. Monophylla from Peninsular Malaysia Species reference. Calanthe monophylla Ridl. [51] and Calanthe taenioides J.J.Sm. [51,52].
Distribution. Distributed in Bangladesh, India, Thailand, Myanmar, Vietnam, Laos, Indonesia, and Malaysia. In Malaysia, the plant was collected from Kedah in the northern part of Peninsular Malaysia (Fig 7). Etymology. The genus name commemorates the Spanish explorer Don Luis de Torres (-1493) who was an interpreter for Christopher Columbus on his first voyage to the Caribbean [53]. The species epithet, brachystachys is from the Greek, brachys means short, whereas stachys means an ear of corn [43]; alluding to the short flower spike of this species.
Habitat and ecology. Grow on tree trunks at tops of a conglomerate hill forest with elevation of 600 m.
Etymology. In Latin, Habena means reins referring to the long, strap-like divisions of the petals and labellum [43]; rostellifera derived from rostellum, a beak, referring to the beak-like and protruding rostellum [55]. . Both H. rostellifera and the following species, H. rostrata, have ovaries with a prominent beak which can also be clearly seen in the fruiting stage [55]. The tongue in front of the rostellum was regarded as an outgrowth of the labellum as shown by [56]. Reichenbach regarded this protruding structure as part of the rostellum, which the epithet name rostellifera was coined after this prominent character [55,57].
Distribution. The first specimen was collected from the 4 th Division, Gunung Mulu National Park by Nielsen in 1978 [60]. Since then, there was no further record on its recollection, until now. Our specimen was collected from Kapit, Sarawak (Fig 11).
Etymology. In Greek, bryon means moss and bios as in the English 'bios' means life [43]. The species epithet cordiferum (latin) means cordate, heart-shaped, with the notch at the base, referring to the heart-shaped labellum [61].
Habitat and ecology. Mixed forest on sandy soil with scattered limestone rock [60], and along the riverine forest with alluvial vegetation (Fig 12).
Distribution. So far, the species has only been recorded in Peninsular Malaysia and Borneo [25,41] (Fig 14). However, the occurrence is still not well-known. Due to the inconspicuous appearance of these plants, small, recurrently occurring high in the forest canopy with small short-lived flowers, they are easily overlooked in the field and often preserved in poor conditions [63].
Etymology. In Greek, tainia means fillet and phyllon means leaf, and Taeniophyllum referrring to the long filamentous leaves of the plant [43]. Meanwhile, the species epithet, rugulosum, in Latin, ruga means finely rugose, referring to the roots having many small wrinkles.
Habitat and ecology. The plant was growing as epiphytes in a lowland riverine forest, on a common riverine tree. Plants were growing on twigs about 3 cm thick. Taxonomic notes. Taeniophyllum rugulosum is belonging to subg. Codonosepalum sect. Sepalocodon, a group characterised by having sepals and petals adnate at base and bracts alternate [64]. Our specimen is characterised by the flattened roots, flattened 2-ranked and alternate bracts, yellowish-green and flowers 5 mm long, triangular tepals and labellum, sepals and petals basally fused into a tube, and the free part of sepals always longer than tube. Some of these characters are also shared with the closely-related species, T. campanulatum Carr, T. intermedium Carr, and T. stella Carr. The absence of incurved spine on the labellum and the wrinkled roots differentiate T. rugulosum from T. stella [63].